AFNI program: 24swap

Output of -help

Usage: 24swap [options] file ...
Swaps bytes pairs and/or quadruples on the files listed.
Options:
-q Operate quietly
-pattern pat 'pat' determines the pattern of 2 and 4
byte swaps. Each element is of the form
2xN or 4xN, where N is the number of
bytes to swap as pairs (for 2x) or
as quadruples (for 4x). For 2x, N must
be divisible by 2; for 4x, N must be
divisible by 4. The whole pattern is
made up of elements separated by colons,
as in '-pattern 4x39984:2x0'. If bytes
are left over after the pattern is used
up, the pattern starts over. However,
if a byte count N is zero, as in the
example below, then it means to continue
until the end of file.

N.B.: You can also use 1xN as a pattern, indicating to
skip N bytes without any swapping.
N.B.: A default pattern can be stored in the Unix
environment variable AFNI_24SWAP_PATTERN.
If no -pattern option is given, the default
will be used. If there is no default, then
nothing will be done.
N.B.: If there are bytes 'left over' at the end of the file,
they are written out unswapped. This will happen
if the file is an odd number of bytes long.
N.B.: If you just want to swap pairs, see program 2swap.
For quadruples only, see program 4swap.
N.B.: This program will overwrite the input file!
You might want to test it first.